The United Nations estimates that Islamic State and related groups have at least 25,000 foreign fighters from more than 100 countries. According to data from the U.S. Counterterrorism Center, Islamic State has already recruited hundreds of people from Tajikistan and Kyrgyzstan and more than 1,000 men from Kazakhstan.

"Just last week we learned that the chief of Tajikistan's counter-terrorism program, someone highly trained by the United States government, abandoned his post to join ISIS," said Rep. Christ Smith of New Jersey.

Experts say some of the challenges that Central Asian governments face are of their own making: widespread corruption, lack of the rule of law and violation of human rights. Unemployment and poor economic prospects add to popular discontent. Radical groups exploit these factors to attract young people to their cause.

The United States is working with regional governments to prevent the dissemination of terrorist messages through social media and the cross-border flow of fighters.

"While there are no reliable statistics, research suggests that the vast majority of Central Asian fighters in Syria and Iraq are recruited while outside their own countries, mostly while they are in Russia, where millions of them live as migrant workers," said Daniel Rosenblum, Deputy Assistant Secretary of State for Central Asia.

Experts say there is no simple solution to the problem, but a key long-term effort must include improving the economic prospects so young people can work at home, where radicalization is less likely to take place than in migrant communities.

While the United States can help in that effort, some say that the real solutions will be local.

"They are the ones closest to the action. They are the ones who know their communities and they are the ones who are ultimately going to either detect and/or prevent, or respond to an incident," said Frank Cilluffo of George Washington University.

Experts say that governments in Central Asia and elsewhere also must improve their human rights record and prevent marginalization of minorities.